Photoelectric properties of magnetically sensitive MOS structures

The photoelectric properties of MOS structures having compensation regions near the field electrode have been studied experimentally. It is shown that the presence of such regions can lead to the appearance of a number of features in the integrated photoelectric properties: the presence of a large photovoltage signal in enhancement, dependence of the form of the photovoltage frequency dependence on the intensity of the light flux, and distortion of the shape of the photovoltage signal in inversion. The presence of compensation regions can be established using measurements of the distribution of the photovoltage over the area of the structure and measurements of the voltage dependence of the phase of the integrated photovoltage signal. The increase or decrease of the photovoltage signal in enhancement after exposure to a weak magnetic field is due to the rearrangement of the impurity-defect structure in the near-surface layer of the semiconductor, leading to the appearance of compensated semiconductor regions near the field electrode. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 82–87, May, 1998.     

Inelastic electron tunneling spectroscopy on MOS structures with very thin oxide films

Inelastic electron tunneling spectroscopy at 4.2 K was used to investigate the defect structure of MOS capacitors with very thin SiO₂ films. Samples were degeneratelyP-andB-doped Si substrates, oxidized in O₂ at 600°C and provided with evaporated Pb, Au, In, Al or Mg electrodes. The observed peaks in the second derivative of theI-U characteristic were assigned to the excitation of phonons and of vibrational modes of the dopants and impurities. The results were found to correlate with infrared data. In addition, a distinct effect of Si/SiO₂ interface states on the characteristic was found.     

Low-energy elementary surface excitations of symmetric films of liquid4He atT=0 K

It is known that low-energy elementary excitations of symmetric films of liquid⁴He atT=0 K are characterized by a momentum q parallel to the surface and may be described by bound states. We have evaluated wave functions and energies of these states for both best short-ranged and optimal long-ranged correlations. Quantities of physical interest may be expressed in terms of these eigenstates and, in particular, for very small momenta (q<0.2 Å^–1) they are mainly determined by the contribution due to the lowest-lying one. We propose analytic expressions for the lowest-lying excitations and fluctuations in the long-wavelength limit. It is proved that in this limiting case, the excitation energy _LW(q) and the averaged static structure functionS _LW(q) should go linearly to zero asq0, whereas the averaged direct correlationX _LW ^Dg (q) should diverge at the origin as 1/q. It is shown that numerical solutions exhibit the expected long-wavelength behavior provided that optimal correlations are used. All these results are displayed in a series of figures and are discussed in detail.     

Interface states and impurities in MOS structures with very thin tunneling barriers

Electron tunneling spectroscopy was used to investigate MOS junctions with very thin silicon oxide or silicon oxynitride layers (2–5 nm) as tunneling barriers. For the tunneling measurements at 4.2 K highly degenerate P-doped (3×10²⁰ cm^-3) Si substrates, oxidized in dry oxygen at 600°C were used. Silicon oxynitride layers were prepared by plasma nitridation in an NH₃ discharge. As gate electrodes evaporated films of Al, Au or Pb were utilized. Changes in the tunneling conductivity were attributed to changes in the density of interface states, caused by hydrogen annealing or by high field stress. The results indicate a correlation between the generation of interface states and the removal of Si-H configurations. Vibrational modes of phonons, dopants and impurities were detected by inelastic electron tunneling spectroscopy.     

Study of density of interface states in MOS structure with ultrathin NAOS oxide

The quality of the interface region in a semiconductor device and the density of interface states (DOS) play important roles and become critical for the quality of the whole device containing ultrathin oxide films. In the present study the metal-oxide-semiconductor (MOS) structures with ultrathin SiO₂ layer were prepared on Si(100) substrates by using a low temperature nitric acid oxidation of silicon (NAOS) method. Carrier confinement in the structure produces the space quantization effect important for localization of carriers in the structure and determination of the capacitance. We determined the DOS by using the theoretical capacitance of the MOS structure computed by the quantum mechanical approach. The development of the density of SiO₂/Si interface states was analyzed by theoretical modeling of the C-V curves, based on the superposition of theoretical capacitance without interface states and additional capacitance corresponding to the charges trapped by the interface states. The development of the DOS distribution with the passivation procedures can be determined by this method.     

Stark-hyperfine measurements in K = 0 and K = 1 states of NH3

High-resolution Stark-hyperfine transition measurements have been made on the J = 1, K = 0 and J = 1, K = 1 levels of ammonia using molecular beam electric resonance spectroscopy. The dipole moments measured are μ(J = 1, K = 0) = 1.47149(15) D and μ(J = 1, K = 1) = 1.47179(15) D. The polarizability anisotropy was found to be positive and hyperfine properties for both states were accurately measured.     

Near-interface oxide traps in 4H–SiC MOS structures fabricated with and without annealing in NO

Near-interface oxide traps(NIOTs)in 4H–Si C metal–oxide–semiconductor(MOS)structures fabricated with and without annealing in NO are systematically investigated in this paper.The properties of NIOTs in Si C MOS structures prepared with and without annealing in NO are studied and compared in detail.Two main categories of the NIOTs,the"slow"and"fast"NIOTs,are revealed and extracted.The densities of the"fast"NIOTs are determined to be 0.76×10~(11)cm~(-2)and0.47×10~(11)cm~(-2)for the N_2 post oxidation annealing(POA)sample and NO POA sample,respectively.The densities of"slow"NIOTs are 0.79×10~(11)cm~(-2)and 9.44×10~(11)cm~(-2)for the NO POA sample and N_2POA sample,respectively.It is found that the NO POA process only can significantly reduce"slow"NIOTs.However,it has a little effect on"fast"NIOTs.The negative and positive constant voltage stresses(CVS)reveal that electrons captured by those"slow"NIOTs and bulk oxide traps(BOTs)are hardly emitted by the constant voltage stress.     

Effect of oxide thickness on the capacitance and conductance characteristics of MOS structures

In this work, the investigation of the interface states density and series resistance from capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics in Au/SnO₂/n-Si (MOS) structures prepared at various SnO₂ layer thicknesses by spray deposition technique have been reported. It is fabricated five samples depending on deposition time. The thicknesses of SnO₂ films obtained from the measurement of the oxide capacitance in the strong accumulation region for MOS Schottky diodes are 37, 79, 274, 401, and 446 Å, for D1, D2, D3, D4, and D5 samples, respectively. The C–V and G–V measurements of Au/SnO₂/n-Si MOS structures are performed in the voltage range from −6 to +10 V and the frequency range from 500 Hz to 10 MHz at room temperature. It is observed that peaks in the forward C–V characteristics appeared because of the series resistance. It has been seen that the value of the series resistance R_s of samples D1 (47 Ω), D2 (64 Ω), D3 (98 Ω), D4 (151 Ω), and D5 (163 Ω) increases with increasing the oxide layer thickness. The interface state density D_it ranges from 2.40×10¹³ cm⁻² eV⁻¹ for D1 sample to 2.73×10¹² cm⁻² eV⁻¹ for D5 sample and increases with increasing the oxide layer thickness.     

Long-wavelength behavior of the optimal HNC/O solution for the ground-state of homogeneous liquid4He atT=0 K

The long-wavelength behavior of the two-body correlation factor,u(k), of the ground-state wave function for an homogeneous liquid⁴He at zero temperature is studied. The solutions are obtained from a paired-phonon-analysis within the HNC/O approximation. The cut-off for the phonons is investigated analyzingu(k) at small momenta. It is shown that the numerical results: (a) rule out a pure gaussian cut-off and (b) are in good agreement with the exponential cut-off suggested by Chester and Reatto. The first-sound velocityc ₁ and the cut-off momentumk _c are determined at several densities in the range 0.016–0.025 Å^–3. In addition, a parametrization of these quantities as a function of the density is provided.     

A novel device layout for tunneling spectroscopy of low-dimensional electron systems

We report tunneling spectroscopic investigations on a barrier separated double-electron-layer system using a novel selective depletion scheme based on self-aligned side gates. We show that the side gate technique is also suitable to impose a tunable lateral confinement on a narrow channel. From the study of tunneling processes on a single-wire device we conclude that the energetic spacing of the one-dimensional subbands can be varied from effectively zero to up to 6 meV. A simple electrostatic model confirms the order of magnitude of the measured one-dimensional level spacing.     

Precision spectroscopy with coherent dark states

Received: 14 September 1998     

Influence of quantum well states on transport properties of double barrier junctions

A strong asymmetric behavior in the I–V characteristics and the tunnel magnetoresistance in asymmetric magnetic double-barrier junctions is predicted. This effect relates to formation of quantum well states in the middle metallic layer. The influence of the random fluctuations of the barrier and the middle metallic layer thickness on the statistics of resonant levels is investigated.     

Calculation of spectroscopic data for the ν = 2 and ν = 3 states of nitric oxide

The calculation of line positions, energy levels and line intensities for the NO overtone bands 2-0 and 3-0, done for the AFGL atmospheric trace gas data tape, is presented. A simultaneous least-squares fit has been made to the measured frequencies of the overtone bands, using previously determined constants for the ground (ν = 0) state. This has resulted in new spectroscopic constants for the ν = 2 and ν = 3 states. The eigenvectors were used to compute line intensities, while the same line halfwidths were used for the fundamentals as for the overtone bands.     

Order and disorder lines in systems with competing interactions: I. Quantum spins atT=0

In the parameter space of systems with competing interactions there are specific trajectories called order (disorder) lines. Along these trajectories the competition between the different interactions effectively reduces the dimensionality of the system and the model can be exactly solved. It is shown that the order (disorder) trajectories end up at a multicritical point. The method of Peschel and Emery is used to determine the (anisotropic) critical behavior of the spin-spin correlation functions near the multicritical point. The quantum spin systems discussed here include theXYZ chain in a field, the straggeredXYZ chain in a field, and a Hamiltonian version of a three-dimensional Ising model with biaxial competing interactions.On leave from and address after September 1, 1982: Institute for Theoretical Physics, Eötvös University, Puskin U. 5-7, 1088 Budapest, Hungary.     

Electroluminescence of silicon nanocrystals in MOS structures

We have studied the structural, electrical and optical properties of MOS devices, where the dielectric layer consists of a substoichiometric SiO_x (x<2) thin film deposited by plasma-enhanced chemical vapor deposition. After deposition the samples were annealed at high temperature (>1000 °C) to induce the separation of the Si and the SiO₂ phases with the formation of Si nanocrystals embedded in the insulating matrix. We observed at room temperature a quite intense electroluminescence (EL) signal with a peak at ∼850 nm. The EL peak position is very similar to that observed in photoluminescence in the very same device, demonstrating that the observed EL is due to electron–hole recombination in the Si nanocrystals and not to defects. The effects of the Si concentration in the SiO_x layer and of the annealing temperature on the electrical and optical properties of these devices are also reported and discussed. In particular, it is shown that by increasing the Si content in the SiO_x layer the operating voltage of the device decreases and the total efficiency of emission increases. These data are reported and their implications discussed. Received: 31 August 2001 / Accepted: 3 September 2001 / Published online: 17 October 2001     

Theory of tunneling spectroscopy in

We calculate the surface density of state of iron based LaFeAsO_1-xF_x superconductor. The gap function is obtained microscopically by solving the Eliashberg equation in a 5-band Hubbard model with the random phase approximation (RPA). Although the gap function has a sign change between Fermi surfaces, we cannot find zero bias conductance peak for [1 0 0] and [1 1 0]-oriented interface.     

Importance of complex band structure and resonant states for tunneling

The paper aims at understanding the tunneling process in epitaxial magnetic tunnel junctions. Firstly, we stress the importance of the complex band structure of the insulator for the tunneling of the metal electrons. For large insulator thicknesses the tunneling current is carried by very few states, i.e., those states in the gap of the semiconductor having the smallest imaginary component of the k-vector. In the case of GaAs, ZnSe and MgO these are Δ₁-states at the -point. Secondly, we discuss the role of resonant interface states for tunneling. Based on simple model calculations and ab initio results we demonstrate that for symmetrical barriers the minority conductance can be dominated in an intermediate thickness range by few ‘hot spots’ in the surface Brillouin zone, arising from resonant interface states. In these hot spots full transmission can still be obtained, when all other states are already strongly attenuated, so that the usual exponential decay can be considerably delayed.     

A survey ofΔK=0 dipole transitions from low lyingJ=1 states in rare earth nuclei

High resolution photon scattering experiments on various Nd-, Gd-, Dy-, Er- and Yb-isotopes yielded new information about the energy and absolute ΔK=0 groundstate transition strengths ofJ=1 levels with excitation energies between 1.5 and 4 MeV. The lowest of theseJ ^π=1^? states are suggested to be the bandheads of aK ^π=0 ^? octupole vibrational band, whereas the origin of the higher lying states is unknown.     

High-spin states in the A= 39 mirror nuclei 39Ca and 39K

High-spin states of the mass A= 39 mirror pair ³⁹K and ³⁹Ca were investigated via the fusion-evaporation reaction ²⁸Si +¹⁶O at 125 MeV beam energy. The Gammasphere array in conjunction with the 4π charged-particle detector array Microball and neutron detectors was used to detect γ rays in coincidence with evaporated light particles. The results of the first high-spin study of the T _z=−1/2 nucleus ³⁹Ca are discussed in terms of mirror symmetry and compared to spherical shell-model calculations in the 1d _3/2–; 1f _7/2 configuration space. Received: 18 August 1999     

k//=0 filtering effects in ballistic electron transport through sub-surface GaAs–AlGaAs double barrier resonant tunneling structures

In ballistic electron emission microscopy on Au–GaAs double barrier resonant tunneling diodes, electrons are transferred across an interface between an area of high and low effective mass and subsequently through a low-dimensional state. Experimentally, the resonant level in the double barrier structure becomes evident as clear step in the ballistic current measured as a function of sample bias. To analyze the spectrum, an extended transfer matrix method, together with the commonly accepted Bell Kaiser model is used. In terms of this model we show that only electrons with zero wave vector parallel to the barriers can be transmitted resonantly.